1. Field of the Invention
This invention relates generally to telecommunications, and more particularly, to wireless communications.
2. Description of the Related Art
Communications systems typically comprise software and hardware, including a variety of analog and digital electronic circuits. To improve performance of communication systems, old circuit designs are routinely replaced with new designs that meet specifications for more advanced products. However, one constant goal is to reduce costs of the circuits to be competitive in the market. Therefore, the product circuit designers are generally searching for creative ways to reduce the cost of the electronic circuitry and systems. One means to reduce the costs is to use only one type of analog hardware. For example, in reconfigurable or tunable circuits, one type of reconfigurable matching circuits has been routinely used to serve different frequency bands. A reconfigurable matching circuit may optimize the performance of an analog circuit to the instantaneous operating frequency band. This “one hardware” approach leads inherently to a reduction in cost for the hardware due to higher volume, less design risk and design time and less liability.
To implement reconfigurable matching circuits, continuous variable components like varactors, variometers and potentiometers and/or switching components like relays, switches and PIN-diodes are usually deployed. One problem with continuous variable components or elements is that they have relatively low maximum ratings for power and current, which generally limits their use to low-power stages. As a result, reconfigurable elements for higher power and current are not readily available. One type a reconfigurable element that may be used with higher power and current is bulky, expensive and cannot be integrated into an analog circuit because they lack a form and fit equivalent to other surrounding circuits.
A matching process generally involves a start impedance, for example, the low output impedance of a RF power amplifier, which is to be transformed to an end impedance, for example, a commonly used 50 Ohm system. Matching of the impedance may be achieved by using one or more matching reconfiguration elements with characteristic impedances that lie between the start and the end impedance. One particular disadvantage of such reconfigurable elements is their low maximum rating for power and current, which limits use of this matching to low-power stages. In other words, this matching process may not be optimized to the extent desired for reducing the current and/or DC-dissipation load of the matching reconfigurable components. Thus, for medium or high power applications, the traditional design approach, that results in, with a single dedicated hardware for a particular dedicated frequency band, is still valid.
For example, growth of wireless communication systems has increased the demand for highly efficient analog circuits, such as power amplifiers including radio frequency (RF) power amplifiers. A power amplifier is an active, two-port device that exhibits both linear and non-linear behavior. Some design parameters for RF power amplifiers include high output power, high linearity, and good efficiency.
Moreover, newer technologies demand transmission of large amounts of data with only a small portion of the spectrum being used. This may be accomplished using sophisticated modulation techniques, leading to wide, dynamic signals that benefit from linear amplification. For instance, some modern wireless applications, such as those based on the Wideband Code Division Multiple Access (WCDMA) standard, use non-constant envelope modulation techniques with a high peak-to-average ratio. In many modern mobile communication networks, however, the transmission gets more and more complex using higher power levels.